Abstract: A sewing machine having an edge guide for producing a stitched seam along an edge of a workpiece terminating at another edge forming an angle with the first has an optical device for directing a pencil or beam of light toward a reflective surface which underlies the workpiece and is covered thereby until the movement of the workpiece exposes the reflective surface at this other edge. The optical detector then produces a signal for initiating a control function, e.g. the change of stitch pattern to tie off the end of the previously sewn seam or to lodge the needle in the fabric so that the workpiece may be turned to bring the other edge into contact with the edge guide. The control system can include a programmer for the successive stitching operations which are initiated in succession in response to the optical sensor.